TCP-Server example - Call a Method of Class / ServerSocket, Static reference to instance method:...


i am new with XoJo and i am trying to write a small TCP server. It handles a few connections and i want be able to send data or close specific connections from a Form. So i used ServerSocket. For example i have connected clients 1, 2, 3, 4, and 5 and want to close the TCP-connection to client 2.

Problem: I want to do this from a timer which cares about the state of the clients.

I tried a lot, like
Call IncommingClientSocket.Close i
where i is the ID of the object.

But i get an error:
Static reference to instance method: call this on an instance of class SocketCore.

Is this a problem of ServerSocket/TCPSocket or do i make a mistace with handling the class?
Please help, thank you.

Here you can download the project:

Here’s the documentation on how to use SocketCore.Close:

You need to call Close() on the IncommingClientSocket (TCPSocket), not the IncommingSocket (ServerSocket).

In your project, look at the IncommingSocket.AddSocket event. Here, you’re creating a IncommingClientSocket instance named “Rueckgabe” and returning it. You need to keep a reference to the “Rueckgabe” instance somewhere that can be accessed from the Timer, and then call its Close() method when you want to close it:


Hello Andrew,
how to save/keep the reference to Rueckgabe?
Can you give me a code-example or the needed steps, please?
Please note: I want to call something like Rueckgabe.Close() with an index to the socket should be closed.
Or can you somewhere upload changed project?

Add a property to the Modude_Modbus module, e.g. clientlist(20) As IncommingClientSocket. Then, in the Addsocket event, add the “Rueckgabe” instance to it:

Function AddSocket() As TCPSocket
//  Dim Rueckgabe As TCPSocket = New IncommingClientSocket(AktSocketNummer) //no
  Dim Rueckgabe As New IncommingClientSocket(AktSocketNummer) // yes

  clientlist(AktSocketNummer) = Rueckgabe // store Rueckgabe
  Return Rueckgabe
End Function[/code]

Then get the reference back in the DataTimeoutTimer.Action event:

[code]Sub Action()
  ' Check if data-timeout. If yes, disconnect client
  Dim i As Integer
  For i=1 To 20
    If DatenTimeout(i)>0 Then
      ' If timeout, then disconnect client
      If DatenTimeout(i)=1 Then
        System.DebugLog "Timeout: " + Str(i)

        Dim Rueckgabe As IncommingClientSocket = clientlist(i) // retrieve Rueckgabe 
      End If 
    End If
  Next i  
End Sub

Hello Andrew,

thank you for quick help - it works :slight_smile:


  • I had to add the property at module Module_Modbus ClientList(20) As TCPSocket
  • To disconnect a TCP connection i had to use the Rueckgabe.Disconnect instead of Rueckgabe.Close.
  • I had to change/leave also

Dim Rueckgabe As TCPSocket = ClientList(i) // retrieve Rueckgabe Rueckgabe.Disconnect

I will upload the new version next days. So this is a TCP-Server-Example with multiple connections (unfortunately not included in TCP-examples of XoJo).

To access TCPSockets created using a ServerSocket you would use the ActiveConnections Method and cast the TCPSocket to your subclass.

Your problem at

' PROBLEM HERE: Call IncommingClientSocket.Close i

should become

' PROBLEM HERE: IncommingSocket.ActiveConnections(i).Close

You can cast the TCP socket to your subclass by casting it as below

Dim Rueckgabe As IncommingClientSocket = IncommingClientSocket(IncommingSocket.ActiveConnections(i))

See for more info.